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We give here references for the instrumental properties assumed in PSF
computations, with particular attention to coronagraphic optics. It also notes
several places where the current models or available files are limited in some
manner that might be improved in a future release.

Note: The WebbPSF software and all of its associated data files are entirely ITAR-free.

Note: The provided files included no header metadata, and in particular no
pixel scale, so one was assumed based on the apparent pupil diameter in the
files. The estimated uncertainty in this scale is 1 part in 1000, so users concerned with measurements of PSF FWHMs etc at that level should be cautious.

The current model pixel scale, roughly 6 mm/pixel, is too coarse to resolve well the edge roll-off around the border of each segment. We make no
attempt to include such effects here at this time. An independent study using much more finely sampled pupils has shown that the effect of segment edge roll-off is to scatter ~2% of the light from the PSF core out to large radii, primarily in the form of increased intensity along the diffraction spikes (Soummer et al. 2009, Technical Report JWST-STScI-001755)

The coronagraph optics models are based on the NIRCam instrument team’s series of SPIE papers describing the coronagraph designs and flight hardware.
(Krist et al. 2007, 2009, 2010 Proc. SPIE), as clarified through cross checks with information provided by the NIRCam instrument team (Krist, private communication 2011). Currently, the models include only the 5 arcsec square ND acquisition boxes and not the second set of 2 arcsec squares.

Weak lenses: The lenses are nominally +- 8 and +4 waves at 2.14 microns. The as built defocus values are as follows based on component testing: 7.76198,
-7.74260, 3.90240.

NIRISS filter bandpasses are assumed to be precisely identical to NIRCam for the filters in common. The exceptions are F158M, which was a TFI filter, for which I retain the cryo transmission curve as measured by the manufacturer (Barr/Materion), and F380M, which is a new filter still in process of fabrication, for which I include a nominal design filter transmission curve.

Occulting spots: Assumed to be perfect circles with diameters 0.58, 0.75, 1.5, and 2.0 arcsec. Doyon et al. 2010 SPIE 7731. While these
are not likely to see extensive use with NIRISS, they are indeed still present in the hardware, so we retain the ability to simulate them.

Where possible, instrumental relative spectral responses were derived from the
Pysynphot CDBS files used for the JWST Exposure Time Calculators (ETCs),
normalized to peak transmission = 1.0 (because absolute throughput is not
relevant for PSF calculations). Not all filters are yet supported in Pysynphot,
however.

Note on MIRI filters: The MIRI instrument team requested that at this time
we release only idealized top-hat function filter profiles rather than the
measured transmissions. We thus take the properties of these filters from the
table at http://www.stsci.edu/jwst/instruments/miri/filters/filters_temp.html .
Internal testing at STScI indicates that with this simplification compared
against the measured filter profiles, systematic errors in computed PSF FWHMs
are typically <1.5% assuming sources with Rayleigh-Jeans spectra at
these wavelengths; systematics in encircled energy are generally <1%.

In summary for the following subset of filters we take information from alternate sources other than the CDBS:

The above filters’ throughputs do not include the detector QE or OTE/SI optics throughputs versus wavelength (or the throughput of the
Germanium FQPM substrates for the MIRI coronagraphic filters). All other filters do include these effects to the extent that they are accurately
captured in the Calibration Database in support of the ETCs.